A generation of music icons is hitting retirement age, along with their baby-boomer fans. Is it time for Bob Dylan to hang up his hat and harmonica?

Last Friday night, Bob Dylan chugged through "Highway 61 Revisited" at the Borgata, an Atlantic City, N.J., casino. His always-raspy voice, now deteriorated to a laryngitic croak, echoed through the no-frills ballroom. Security guards wandered the seated audience, enforcing his no-cameras policy. Behind some empty rows in the rear, a handful of dancers shimmied mildly. A trickle of people peeled off for the exit, descending an escalator into the ringing rows of slot machines. One of the walkouts, 50-year-old Warner Christy, said he wouldn't be paying to see the singer again: "I've been scared straight."

illustration by Mick Coulas

For people of influence in any walk of life, from corporate leaders to sports stars, the question of when to leave the stage is a crucial one. Do you go out at the top of your game, giving up any shot at further glory? Or do you dig in until the end, at the risk of tarnishing a distinguished career?

For the many and passionate fans of Bob Dylan these are questions that loom large. After 50 years in music, his place in the pantheon is unassailable. He is the age's iconic singer-songwriter and rock's poet laureate—a title even he lays claim to in the introduction read aloud before his concerts. And unlike other artists of the '60s who've been trading on nostalgia since the '70s, he has continued to release new material and wrestle with his art form.

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Such are the consolations for fans who have seen one of music's best talents at his worst. The issue of whether Mr. Dylan should pack it in has been an enduring parlor game in music circles, whether part of the punk generation's attack on hippie dinosaurs, or the dismay of those hippie dinosaurs over their hero's notoriously dismal output in the '80s. Now, however, Mr. Dylan's detractors question whether he—at age 69 and having just wrapped yet another tour—is capable of another turnaround.

Most alarming to listeners devoted to his seminal recordings: the state of Mr. Dylan's voice, decades on from its first signs of deterioration. Dr. Lee Akst, director of the Johns Hopkins Voice Center, says it's impossible to diagnose Mr. Dylan without an examination, but that rock singers are especially prone to scarring or other damage to the vocal cords. Such trauma can be cumulative, he says, compounding the risks for the perennially touring singer. What's obvious: Though he never had a conventionally pretty voice—that was part of its power—lately he's been sounding like a scatting Cookie Monster. On stage, he strums an electric guitar and blows on a harmonica but spends more time at an upright organ, vamping.

This classic was released in 1963.

Representatives for Mr. Dylan said he was unavailable for comment.

Retirement is an alien concept among music stars who know only a life of performing and touring. Those who have decided to give it up early have often changed their minds. Saying it was time to "move aside," Little Richard announced his retirement at age 70—eight years ago. Since then, he has played about 100 gigs. At age 33, rapper Jay-Z said he was hanging up his microphone to concentrate on being a music executive. Three albums later, he vows to never make such a pronouncement again, recently saying, "I lost the privilege to even discuss the topic, I did it so bad." At the zenith of his Ziggy Stardust fame, David Bowie announced his last concert from the stage, only to reinvent himself with impressive results. Yet he has not publicly performed since 2007, and perhaps won't ever again—he hasn't said.

illustration by Drew Friedman

This issue is coming to the fore now that a generation of performers is hitting old age, along with their baby-boomer fans. Not unlike their R&B predecessors, such as the still-touring Four Tops, most classic rock acts are delivering note-for-note nostalgia, but on a bigger scale. Pink Floyd's Roger Waters scored one of the most successful tours of the year by rolling out "The Wall," updating only the 1980 stage technology. But for the handful of acts releasing new material and trying to stay relevant as artists, there's no late-career blueprint.

Mr. Dylan isn't working toward a golden parachute; he's pursuing a craft. "Anybody with a trade can work as long as they want. A welder, a carpenter, an electrician. They don't necessarily need to retire," he said in an interview published in Rolling Stone last year. "My music wasn't made to take me one place to another so I can retire early." After all, he cut himself from the same cloth as artists such as Woody Guthrie and Leadbelly, for whom performing was a matter of existential, if not economic, necessity.

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Jerry Lee Lewis, 75

Jerry Lee Lewis, now.
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One of last active members of rock 'n' roll's freshman class, the Killer has been busy with a Broadway cameo in "Million Dollar Quartet" and a new album featuring rockers old (Mick Jagger)and young-ish (Kid Rock).

Next gig: Jan. 15 at the Horseshoe Southern Indiana in Elizabeth, Ind.

Mr. Lewis, circa 1957.
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Roger Waters, 67

Roger Waters, now.
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By mounting a tour of his brooding rock opera, 1979's "The Wall," this year, the former Pink Floyd singer tapped a big audience: former—and current—angst-ridden teens. The tour ends in England next summer.

Next gig: Friday at the Oracle Arena in Oakland, Calif.

Mr. Waters with Pink Floyd, 1971.
Redferns/Getty Images

Patti LaBelle, 66

Pattie LaBelle in 2008.
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In September, the Grammy-winning singer, best known for the '70s hit "Lady Marmalade," joined the cast of Broadway's "Fela!," playing the beleaguered mother of the titular Afrobeat singer.

A Flock of Seagulls

Mike Score, now.
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Despite a brief reunion of the original band via VH1, this '80s act known for its hairdos and hits such as "I Ran (So Far Away)" is essentially a one-man operation now. Singer Mike Score, age 53, soldiers on witha pickup band.

Next gig: Dec. 30 at the Brixton in Redondo Beach, Calif.

Mr. Score performing with Flock Of Seagulls.
Redferns/Getty Images

He has sold almost 21 million albums since 1991, when Nielsen SoundScan began tracking such figures. In the past decade, he has moved more than 3.7 million concert tickets and grossed more than $192 million on tour, according to Pollstar. If he walks away from touring, he has fallbacks, including painting (the National Gallery of Denmark is exhibiting 40 of his works) and writing (the first volume of his "Chronicles" memoirs was a hit; two more installments are expected.)

Why single out Mr. Dylan when Judy Collins and other graying veterans are out there touring unmolested? Firing the debate is his status as the ultimate music icon, the caretaker of a body of work that, many would agree, stands in contrast to his current sound. He's also got a touring schedule that would put some hungry young acts to shame. He's been doing roughly 100 gigs, year in, year out, since 1988. While some oldies acts play obscure venues because no one else will have them, Mr. Dylan seems bent on playing every last stage in America, including minor-league baseball parks, college campuses and antiquated theaters such as the Shrine Mosque in Springfield, Mo.

Casual fans, especially, are vexed by Mr. Dylan's ongoing habit of mutating his most familiar songs. In Atlantic City he shadowboxed with the beat on "Just Like a Woman," going silent when the crowd gamely sang the chorus, then rushing out the words himself. To his many loyal admirers, such idiosyncrasies just emphasize his artistry. "With every concert, he's saying, 'Think again,' " says historian Sean Wilentz, author of the recent book "Dylan in America."

Jim Waniak is having none of that. Though he's seen eight previous Dylan concerts, he, too, walked out on him at the Borgata, saying, "I know every word to 'Desolation Row' but I couldn't sing along. What you're used to feeling from his music just isn't there."

Mr. Dylan's critics say they're simply evaluating him as he is now, without spotting him any points for past achievements. Last July, music critic Ian Gittins watched Mr. Dylan headline a music festival in Kent, England, where he followed strong performances, including one by folk newcomers Mumford & Sons. At first, Mr. Gittins jostled for a view at the rear of the predominately young crowd. But before the singer even got to his frequent closer, "Like a Rolling Stone," the critic had elbow room to spare. "The crowd had melted away," retreating from "the perplexing noise of this man whining," Mr. Gittins, 48 years old, said in an interview.

Of course, the singer has been derailing expectations, riling the faithful and inspiring calls for his head since he strapped on an electric guitar at the Newport Folk Festival in 1965. He made many of his critics reconsider in 1997, when he released "Time Out of Mind," a mordant, Grammy-winning album that established a new artistic benchmark for him. But if he plows on indefinitely, could the accumulating career lows undermine the highs?

"Listen, this legacy stuff is a bunch of crap," says University of Chicago economics professor David Galenson. "That goes for Michael Jordan and Bob Dylan and economic professors: You're known for your best work, not the bad work at the end of your career."

Mr. Galenson examined the two potential "life cycles" of creativity among great artists in his book "Old Masters and Young Geniuses." Epitomizing the latter, Mr. Dylan worked conceptually and with deliberation, turning out his most influential work before he hit 30.

So what becomes of young geniuses in their dotage? Mr. Galenson judges their "graciousness" by whether they accept that their greatest work is behind them. He points to interviews in which Mr. Dylan discusses searing songs such as "Blowin' in the Wind" with a sort of detached awe. "I give him credit for saying, 'I love those old songs but I couldn't write them anymore if I tried.' My suspicion is that very few artists of any kind would admit that," he says.

Mr. Dylan has defied the young-genius playbook simply by continuing to roam the earth, unlike Jimi Hendrix and Janis Joplin. The result: the somewhat disconcerting spectacle of a rock star acting his age. Mortality has been an undercurrent in his recent music. The song "Forgetful Heart" on last year's "Together Through Life" album features the closing line "The door has closed forevermore, if indeed there ever was a door."

Mr. Wilentz says we're witnessing an unvarnished evolution, pointing out that Mr. Dylan hasn't made obvious fixes with cosmetic surgery, and favors "old man's clothes." With flat wide-brimmed hats and dark suits with piping on his pant legs, "he looks like a cross between a parson and a Mississippi riverboat gambler. It's stagey, but it's certainly sedate."

Pop critic Jim DeRogatis says Mr. Dylan's methods—changing the set list nightly, reshaping songs on the fly—are nobler even in defeat than the crowd-pleasing approach by the Rolling Stones. The Stones have poured money into production on stadium outings, such as the "Bigger Bang" tour in 2006 (featuring tiered balconies on stage for high-end ticket buyers) and delivered faithful renditions from their catalog, from "Start Me Up" to "Brown Sugar." "They're like a global corporation and they cannot let down their stockholders and employees," Mr. DeRogatis says.

Still, Mr. Dylan's live shows are a no-go for the critic ("I've been burned too many times") now that they're not compulsory—Mr. DeRogatis left the Chicago Sun-Times last year.

Stalwarts revel in the promise of resurgence. Two weeks ago, Kenny Goldsmith took his 12-year-old son to his first Bob Dylan concert, at the Mid-Hudson Civic Center, a hockey-rink facility in Poughkeepsie, N.Y. They both left disappointed. Reading the show's set list online the next day, he was surprised to see "Just Like Tom Thumb's Blues"—he hadn't even recognized the lyrics coming out of Mr. Dylan's mouth.

Last week Mr. Goldsmith was in the audience again, this time at Terminal 5, a club frequented by indie rock bands on their way up. The venue was crowded and hot, the sound was clear, and Mr. Dylan seemed fired up for a three-night stand in Manhattan. Occasionally he bared his teeth in either a grimace or a grin.

As Mr. Dylan plowed through the climax of "Tom Thumb's Blues," singing, "I do believe I've had enough," a smiling Mr. Goldsmith turned to a friend and shouted, "Compared to last time? 180 degrees!"

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